Biaxially oriented polyester films are used for a variety of purposes including packaging, industrial, electronic, decorative, label, and imaging applications and often perform multiple functions. For example, biaxially oriented PET films and laminations are popular, high performing, and cost-effective flexible substrates for a variety of film structures used in thermal transfer printing, such as transferring ink to substrates by thermal sublimation.
These films may, for example, be used as a thermal transfer ribbon. The films, for example, may be used in the printing of barcodes or digital photographs on paper or other suitable recipient substrate.
Thermal transfer printing applies to printing processes that utilize heat in order to produce an image by either physical or chemical means or a combination of both (G. Laporte et al., “The Forensic Analysis of Thermal Transfer Printing”, J. Forensic Science, Vol. 48, No. 5 (2003)). Its predominance has evolved in the past three decades with the advent of bar coding, retailer receipts, fax machines, event tickets, high resolution digital photography and plastic identification cards.
Thermal transfer printing is a digital printing process in which material is applied to paper (or some other material) by melting a coating of ribbon so that it stays glued to the material on which the print is applied. FIG. 1 shows an example of a thermal transfer printing process.—(Based on Image from Wikipedia “Thermal Transfer Printing”, http://en.wikipedia.org/wiki/Thermal_transfer_printing). In its simplest form the ribbon is formed from a polymeric substrate and at least one layer of ink coating. As the ribbon moves over the print head, resistive elements on the print head get heated, which causes the ink to melt. As the ink becomes molten, it releases from the substrate film and transfers onto the receiver (print surface). Release happens either via ink sublimation (“dye diffusion thermal transfer” D2T2) or by means of a wax carrier (“thermal mass transfer, TMT). The used ribbon separates from the receiver and is wound up on a take-up spindle.
Spent ribbons constitute a significant waste in the thermal transfer ribbon process. Accordingly, some references have described ribbon recycling methods. See, for example, Chinese patent application CN102582294A. However, these recycling methods show that the complex structure of the thermal transfer ribbon makes it difficult and uneconomical to recycle and recover the polyester component once the ribbons are spent. As a result they end-up usually disposed of by incineration or thrown into a landfill resulting in significant carbon footprint.
Coca-Cola Company's U.S. Patent Application Pub. No. 2009-0246430 A1 states that “It is known in the art that carbon-14 (C-14), which has a half-life of about 5,700 years, is found in bio-based materials but not in fossil fuels. Thus, “bio-based materials” refers to organic materials in which the carbon comes from non-fossil biological sources. Examples of bio-based materials include, but are not limited to, sugars, starches, corns, natural fibers, sugarcanes, beets, citrus fruits, woody plants, cellulosics, lignocelluosics, hemicelluloses, potatoes, plant oils, other polysaccharides such as pectin, chitin, levan, and pullulan, and a combination thereof. The detection of C-14 is indicative of a bio-based material. C-14 levels can be determined by measuring its decay process (disintegrations per minute per gram carbon or dpm/gC) through liquid scintillation counting. This reference also teaches the use of bio-based ethylene glycols and terephthalic acids to form a bio-based polyethylene terephthalate resin useful for beverage bottles.
U.S. Patent Application Publication No. 2010-0028512 A1 describes a method to produce bio-based polyester terephthalate (PET) resin which may then be used to make articles, containers, or packaging for food and beverage products. The application also discloses the use of bio-based polyethylene to produce closures, caps, or lids for bio-based PET containers as well as the use of bio-based polyethylene labels via film extrusion for said containers. However, there is no contemplation of producing bio-based polyethylene terephthalate films for thermal transfer ribbon applications.